With dimensional scaling of semiconductor device, threshold voltage decreases with the reduction of channel length, that is to say, short channel effects arise in semiconductor device. Fin Field Effect Transistor, i.e. FinFET is developed to face challenges from semiconductor design and manufacture.
In a FinFET structure, it is desirable to have a channel region as thin as possible to improve the gate control of the channel and restrain short channel effects. However, while channel thickness is less than 10 nm, carrier mobility will decrease with the reduction of channel thickness, which may deteriorate device performance seriously. Specially, a portion of the channel near the source side may be affected severely, while in the drain side, channel thickness will play a minor role in carrier mobility due to a saturation effect caused by high electric field.
Drain Induction Barrier Lower (DIBL) is an non-ideal effect of short channel devices, that is to say, when channel length decreases, source-drain voltage may increase such that P-N junction depletion regions of source and drain becomes closer and electric line in channel may punch through from source to drain, which may cause decrease of potential barrier in source side and increase of carriers from source to channel and thereby lead to increase of current in drain side. With further reduction of channel length, threshold voltage of transistors may decrease due to increasingly severe DIBL effects, which may result in decrease of device voltage gain and restrict improvement of integration level of Very Large Scale Integrated Circuits (VLSIC). It is desirable to have a channel thickness, specially the channel thickness near the drain side as thinner as possible to depress DIBL effects.
Therefore, an asymmetric FinFET device and method of fabricating the same are provided to balance the effects on carrier mobility and DIBL by channel thickness and improve device performance as well. Specifically, the thickness of the portion of the channel near the source side is 1-3 times the thickness near the drain side, and the length of the relative thin portion of the channel is 1-3 times the length of the relative thicker portion. That is to say, the channel has a larger thickness near the source side in regard of the effects by carrier mobility by channel thickness; while in the drain side, because the channel width has a small effect on carrier mobility, the channel has a smaller thickness to suppress effects of DIBL. Comparing with the prior art, the harmful effects of short channel effects can be effectively restrained by the present invention and the device performance can be improved.